C++ :: Parsing Txt File - How To Chop Strings Into Meaningful Characters

Are there any examples how to parse a matrix:

Code:

const string ABC = "
A B C D
A 1 -1 2 14
B 0 -2 -4 8
C 6 2 2 3

" so if i have it as a string stream and then loop through each line like this:

Code:
istringstream in (ABC);
for (string line; getline(in, line); ){
vector<char> vec(line.begin(), line.end());
for (int i = 0; i< vec.size(); i++)
cout << vec[i] << "
";
}

I get my strings chopped into characters. but how to chop it into "meaningful" characters so that -1 is not - and 1. is there any quick way for that to happen ??